The invention is based on a fuel injection valve for a vehicle. In a fuel injection valve of this kind, which has been disclosed by GB 1 320 057, the actuating part of the valve member is embodied as being of one piece with this valve member. The valve member of the prior art has a piston as the actuating part. One end face of the piston borders the control pressure chamber, and another end of the piston includes a pressure shoulder which transitions into a smaller diameter part having an end face that forms a sealing face, which controls the injection opening. The pressure shoulder is subjected to the pressure in the pressure chamber, which continuously communicates with the high-pressure fuel reservoir, which in turn continuously communicates with the control pressure chamber by way of a throttle. This control pressure chamber has a second outlet that is controlled by a piezoelectric valve. When the second outlet opens, the pressure in the control pressure chamber decreases to a relief pressure, the relief pressure acts upon the shoulder of the valve member in an opening direction which opens the injection valve.
In a fuel injection valve of this type, there is the disadvantage that a precise metering of the fuel injection quantity over time and the stroke of the fuel injection valve member is not possible. When the injection valve needle opens, it lifts with its sealing face up from the valve seat and at this instant, the high fuel pressure prevailing in the pressure chamber can also act on the sealing face in the opening direction. As a result, the valve member experiences an additional force in the opening direction, which has a serious effect on the dynamic opening behavior of the valve member. The force that acts in the opening direction reaches a limit value by way of the stroke. The progression of force thereby follows an approximately exponential curve. This property impedes the metering of small fuel injection quantities in which a reclosing of the valve member is required before its end position is reached or before the maximal force that acts in the opening direction is reached. A precise metering of fuel injection quantities is primarily impeded in the intermediary stroke region.
With the fuel injection valve according to the invention, it is now possible to better control the opening event of the valve member so that a more precise metering of small fuel injection quantities becomes possible. With the aid of the piston and the hydraulic chamber that is adjoined by the valve member on one end and by the piston one the other end, a stabilizing force is obtained by way of the compensation pressure face on the valve member and this force smooths the opening event of the fuel injection valve member. Immediately upon the first opening movement of the valve member, a pressure builds up in the hydraulic chamber that increases very rapidly to a maximum value, but then remains constant since starting from particular pressure, the position of the piston can change and thus the volume remains constant. In an advantageous improvement of the invention, the piston is equipped with differently sized piston faces so that the initial pressure in the hydraulic chamber is reduced in relation to the reference pressure, wherein if the pressure of the high-pressure fuel source is selected as the reference pressure, a pressure that is smaller by the reduction ratio acts in the closing direction on the compensation pressure face on the valve member. In this manner, an opposing force can be kept essentially constant on the valve member starting from a particular pressure.
Other advantages can be inferred from the following description of an exemplary embodiment.